Manhole cushion



Aug. 4, 1936. s. R. FLORA f MANHOLE CUSHION Filed sept.) 14, 1934 INVENTOR. SAMUEL R. FLORA BYQ @YM ATTORNEY.

Patented Aug. 4, 1936 UNITED STATES PATENT OFFICE MAN HOLE CUSHION Application September 14, 1934, Serial No. '743,942

4 Claims.

The present invention relates to gaskets, and more particularly to manhole, handhole Vand. other cushions and gaskets.

It is well known that manhole covers, partic- 5 ularly those used on the city streets, have been generally made of cast iron and have been machined flat on the lathe on the underside to provide a smooth bearing surface. Experience has shown that ordinarily a new cover tended 1o to fit fairly well and did not rattle, but it was not long before a small stone, dirt, rust, and the like settled underneath an edge of the cover and caused it to unseat. As each vehicle passed l over the cover, a loud and disagreeable rattle l5- Was set up which prematurely wore down the cover. other obstruction, it was usually dinicult to reseat uniformly because portions of the undersurface wore unevenly. It has been found that a rattling manhole cover wore down very rapidly and required replacement in a. few years. Attempts have been made to silence manhole covers and to prevent them from rattling, but serious disadvantages and shortcomings have been 9 5 encountered so that they were not wholly satisfactory in practical use. For example, prior endeavors involvedV a plurality of ax strands which may be wound on a cable machine and then bound with a cotton or cloth webbing. .Tar

or asphalt or a. similar substance was then impregnated thoroughly into the tape. This tape was laid between the flange of the manhole and the cover. It was found, however, that this did not meet the exacting requirements of the practical situation nor the stringent demands of the authorities of cities, towns, villages and the like for an efcient manhole cushion and gasket. Primarily the cushion and gasket was of such a nature that the asphalt or tar stuck both to the 4,0 flange and to the cover. In some cases, of course, this Was desirable, but the cover could not be raised without destroying the gasket. The webbing was very weak and could not withstand friction, shocks or other loads. Thus,

45 when the cover was raised, part of the gasket would stick to the flange and part would adhere to the cover, so that the cushion was torn apart and its utility seriously impaired or even destroyed. This was particularly annoying in the 50 winter, when the asphalt became so hard and adhered so tenaciously due to the low temperature that sometimes the cover could not be raised without breaking it. Great expense was involved in replacing broken covers and .de-

55 stroyed Cushions. Furthermore, it was found Even after the removal of the pebble or that the installation of these prior cushions could only be done at certain times of the year. In winter the asphalt congealed to such a degree that it could not be made to stick properly to the ange or cover, and the asphalt became too hard and brittle and did n ot have the proper plasticity to enable it to conform to the irregularities in the two bearing surfaces. On the other hand, the melting point of the asphalt was about i90 F. so that in summer the asphalt 10 became soft and exceedingly sticky. The Workmen could not handle the tape because it would stick to everything it touched, including the workmens hands and clothing. As a practical matter, installations were so disagreeable that 15 in some instances they were not vmade by the workmen. Thus.I the use o f impregnated ax was confined to a vfew moderately temperatured months. Moreover, the composition of thefprior cushions was ci a flimsy and Weak nature which could not withstand heavy stresses Without rupture. If it were attempted to increase the strength by making the tape heavier and thicker, the increased size of the cushion raised the cover to such a degree that its use was dangerous. A high manhole cover has been known to flip out of its seat so as to leave the manhole open. Likewise people have a tendency to trip over a high cover which projects above the level of the street. For this reason, it is essen,- tial to keep the thickness of the cushion below a certain maximum which is quite small for the conventional street manhole. Prior cushions had the serious disadvantage of being composed of a material which made them too bulky in order to provide sufficient strength and plasticity.

Other suggestions included tire fabric, Vbrake lining material, lead and the like but these did not provide the proper amount of strength combined with plasticity to permit the cushion to conform to the irregularities of the bearing surfaces. These materials likewise did not have the proper adhesive qualities.

Prior cushions and gaskets had the foregoing as well as other shortcomings which rendered their use not wholly satisfactory. Although numerous attempts have been made none, as far as I am aware, have been wholly practical and successful. f

It is an object of the present invention t0 DIQ- vide a manhole gasket which is clean, which is easily handled and which may be installed at any time of the year regardless of temperature changes.

It is another object of the present invention to provide a manhole gasket which has sufficient strength combined with a proper amount of plasticity and packing effect to conform to the irregularities of an unmachined or worn or corroded cover and flange, so as to provide a full bearing surface under the cover at all times.

It is a further object to provide a gasket which may be selectively bonded to the cover and/or flange so that the cover may be raised from time to time without destroying the gasket.

It is also within the contemplation of the present invention to provide a manhole cushion which is inexpensive to manufacture and simple to construct, which will not rot or otherwise deteriorate under outdoor exposure, which will eliminate the necessity of machining the frames and covers, which will naturally take on a circular shape and lie flat on the ange without buckling or falling into the manhole, and which is strong and pliable and yet suiliciently thin to prevent the cover from being seated too high.

Other objects and advantages will become apparent from the following description taken in conjunction with the drawing, in which:-

Fig. l is a diagrammatic cross-sectional view of an embodiment of the present invention;

Fig. 2 illustrates a section view of a manhole and cover; and

Fig. 3 depicts aschematic top plan view of a section of myY cushion.

Referring more particularly to the drawing, reference character l designates a manhole frame for a street or the like having a manhole 2. Around the upper edge of the manhole is the flange 6 which forms a seat for the cover 4. The depth of this seat may vary with different size manholes, but in the conventional manhole, the seat is only slightly deeper than the thickness of the cover. This leaves only a little space in which to insert cushion 'I which fits smoothly around the periphery of the flange.

In Fig. 1, an enlarged detailed view of the cushion is shown. It will be noted that the cushion is built up in layers of material and then folded longitudinally in half. By the use of this arrangement, a natural curvature is effected so that the cushion will seat itself around the periphery of the curved flange without buckling or tending to fall down the manhole, particularly when the cover is being lplaced on.

As a foundation for the cushion, I have provided a screen I0, preferably of a non-corrosive metal such as brass, bronze or the like. The screen may be of a relatively coarse mesh, say of about 5 to 20 mesh and may be laid diagonally as is shown in Fig. 3 in order to provide a suflicient pliability to the cushion. In this manner, the cushion may be bent sufficiently to conform to the curvature of the manhole. If the cushion cannot be made to lie evenly and naturally around the flange, it will tend to fall off into the manhole, making it very diicult to install. The metal screen gives a strong bendable and pliable foundation to my cushion and increases the life substantially. In addition, only a small amount of space is required by the screen so that the cushion may be made considerably thinner than heretofore without loss of strength. This is a great advantage in View of the limited amount of space which is available for a gasket or cushion in the conventional manhole. Prior cushions, as brought out hereinabove, tended to raise the cover too much so that people were likely to trip over the same, and it was even possible for a swift moving vehicle to flip the cover out of the seat.

On each side of the screen, I have provided an asbestos layer l2. 'Ihis may be in the form of an asbestos cloth or the like. I have found that the asbestos and mineral fibers may be made to adapt itself very well to the stringent requirements of a manhole cushion. It packs together well under the load of the passing vehicles and readily conforms to the undulations and irregularities of the cover and flange. A uniform and continuous bearing surface is thus formed. This is particularly valuable in View of the fact that prior gaskets were not as pliable and consequently had more internal friction and more rapid wear. In addition, asbestos is practically unaffected by long exposure to the elements by rotting or otherwise deteriorating.

In order to bind the tape together and provide the required amount of gumminess and resilience, the asbestos is impregnated with a rubber composition.

The rubber composition has a base of rubber such as smoked sheet rubber. A ller of lithopone, pigment or the like is added to give the rubber body a greater plasticity and incidentally to render the substance white. If the cushion is too elastic the manhole cover will continually bounce out of its original position, particularly when first laid, so that a new surface is continually exposed to the cushion. This shifting would prevent the tape from conforming to the irregularities of the bearing surfaces. A small amount of zinc oxide or similar substance is preferably added to take care of the acidity and to thus prolong the life of the rubber. These ingredients are then milled and dissolved in a suitable solvent such as naphtha, benzol, etc. together with a wood pitch or the like. The pitch renders the substance adhesive to any desired extent. In the event that a permanent cushion is to be laid, a greater amount of pitch may be added to insure a more tenacious sealing of the manhole cover. To impregnate the cushion, it is preferably passed through the solution after which it is hung up to permit the solvent to evaporate. The proportions and ingredients of the rubber composition may of course be varied in accordance with special requirements and prices. The proportions in the following schedule have been found satisfactory.

Per cent by weight Rubber 60 Filler of lithopone 20 Zinc oxide 5 Pitch l5 My rubber composition has superior qualities. In summer, it will not melt and become messy and disagreeable to handle. For the same reason,

it forms a very good cushion for steam or other hot manholes. In this event, however, it is generally desirable to reduce the amo-unt of pitch to maintain the same amount of adhesiveness. In winter, my tape will remain soft and pliable so that it may easily be installed regardless of climatic conditions. Likewise, an installed cushion will not congeal in winter to such an extent that the manhole cover can hardly be removed, particularly in an emergency.

Around the outer surface of the rubberized asbestos, I have applied coating I4 and i5 of a similar rubber adhesive. An increased amount of pitch up to about 35-40% according to the desired adhesiveness, is added to the composition.

A small quantity of creosote may be added. The proportions and ingredients may vary according to particular requirements, but the above have given satisfactory results. The coating of adhesive aids in excluding idampness and dirt which might tend to increase the internal friction, corrosion and/or rotting of the cushion.

To one surface of the tape and gummed to the adhesive may be applied, a cushioning layer l1 of a soft elastic material, such as a jute, sponge rubber, ground cork, sawdust, etc. An ordinary gummy sack cloth has been found to work very well since substantially no tensile load must be borne by the layer. A cloth or brous material has been illustrated in the drawing, but it is understood that numerous equivalents may be substituted such as sponge rubber which give the desired cushioning effect.

When the cushioning layer vor pad has been laid, the whole tape is preferably folded longitudinally so that a double layer of the jute or pad is formed. It will be found that the folded tape very easily takes on a naturally curved shape to conform to the shape of the manhole. The cushioning layer, which is then formed in the center of the tape, is suiciently soft and yielding to withstand the continuous and heavy shocks of traffic. Otherwise a hard, unyielding mass is formed which does not provide the same cushioning effect. This is valuable from the point of view of wear on the manhole and the gasket itself.

The outer layer I5 of the adhesive now serves as a binder for the flange and/or cover. If the tape is laid as it is, it will stick to both the flange and cover. However it is not necessary that the gasket be stuck to both the flange and th-e cover. As a matter of fact, it is highly desirable not to have the cover stuck down permanently. In order to prevent the tape from sticking to an adjacent surface, I have laid a protective sheet I8 of crinolin cloth over the outer surface of adhesive. This preferably covers both the top and bottom and may be selectively removed from either side as is desired. When the crinolin sheet is placed over the adhesive surfaces, it is possible to roll up the tape cushion in spools in which form they may be distributed. The cloth may now be removed from one side of the tape so that the exposed side adheres to the flange. The cloth sheet remaining on top prevents the cover from being permanently anchored down. In this manner, if the manhole cover must be removed from time to time, the tape is not affected, nor will it wear or be destroyed by such removal. If the crinolin cloth is of a relatively thin material, the rubber adhesive slightly penetrates through and gently holds down the cover. Thus, when a vehicle passes over the cover, it is not jarred out of position and yet the cover is sufficiently free to be readily raised.

In the event that the cover and flange are both very well worn and quite irregular, it will take only a few passages of an automobile over the cover before the tape takes on the shape of the irregularities therein and provides an even bearing surface. This will make the tape stick, and any number of succeeding passages of automobiles will not destroy the seat.

The ultimate size of the cushion is an important factor with respect to the acceptability by the trade, particularly the street and road bureaus and commissioners, the reliability and the safety. I have constructed my cushion so that it is possible to reduce the size to the preferable dimensions off-3% of an inch by SA of an inch. It is possible, however, to reduce the size to as small as 11g of an inch, if necessary, without unduly weakening the cushion or materially reducing its cushioning effect.

It is to be observed that the present invention provides a manhole cushion which is not affected by temperature changes, is neat, clean and agreeable to install, and permits the cover to be raised at any time of the year without injury.

It is also to be noted that the present invention provides a manhole cushion which is not subject to the deleterious and ruining effects of rain water or summer heat.

Furthermore, the present invention provides a manhole gasket which may be constructed sufficiently thin for safety, and still be adequately strong and pliable.

While the present invention has been illustrated and described with respect to specific embodiments thereof, it is to be observed that modications and variations may be resorted to as those skilled in the art would readily understand. Modifications and variations are within the scope of the present invention as defined in the appended claims.

I claim:-

1. A manhole cushion which comprises a layer of cushioning material, a metallic screen on each side of said cushioning material, a layer of fibrous material associated with each of the sides of said screens, a layer of an adhesive substance super- 3 posed on each layer of said fibrous material, and a protective layer on the uppermost and on the lowermost layer of said adhesive.

2. A manhole cushion which comprises a layer of cushioning material, a metallic screen on each side of said cushioning material, a fibrous material adapted to conform to irregularities of bearing surfaces associated with said screens and impregnated with a rubbery mass, a layer of an adhesive substance on each of the sides of said fibrous material, and a readily removable protective layer on the uppermost and on the lowermost layers of said adhesive.

3. A manhole cushion which comprises a layer of cushioning material having resiliency and strength, a metallic screen on each side of said cushioning material, an asbestous material associated with each of the sides of said screens and impregnated with a rubber and pitch composition, an adhesive layer on each of the sides of said asbestous material on said screens, and a protective layer on the uppermost and on the lowermost layer of said adhesive, said protective layers capable of being selectivelyA removed to permit the exposed layer to adhere to a juxtaposed bearing surface.

4. A manhole cushion which comprises a cushioning layer of soft, elastic material, a metallic reinforcing element on each side of said cushioning layer, an inert element containing mineral fibers associated with said reinforcing elements, a rubber composition impregnating said reinforcing and inert elements and forming an adhesive coating, and a removable protective layer on the uppermost and lowermost surface of said adhesive coating.

SAMUEL R. FLORA. 

